Astronomers Confirm Elias 2-24b as Youngest Known Exoplanet

Astronomers have confirmed the youngest exoplanet ever directly observed, a gas giant called Elias 2-24b that is less than 1 million years old, according to WIRED. The planet orbits a star of the same age roughly 450 light-years from Earth.

A research team led by Andrea Bernardi at Diego Portales University in Chile made the confirmation, WIRED reported. The team compared telescope images taken years apart to show the object is gravitationally bound to its star rather than a background light source or instrument noise.

How did astronomers confirm it was a planet?

The team focused on seven protoplanetary disks that showed gaps in their dense matter, since growing planets are believed to carve out such voids, per WIRED. One gap, around a star called Elias 2-24, had been known for nearly a decade after the European Southern Observatory's Very Large Telescope detected a point of light inside it. That discovery sparked debate over whether the object was a true planet.

Bernardi's team reanalyzed coronagraph data — images in which the central star's light is blocked so dimmer reflected light from nearby objects becomes visible, WIRED reported. Using observations from the W.M. Keck Observatory in Hawaii collected in 2018 and 2020, the researchers compared the object's position across the two years. They concluded it moved in a way consistent with being bound to Elias 2-24, confirming it as a planet rather than an unrelated star or artifact.

What do astronomers know about Elias 2-24b?

Elias 2-24b orbits its star at approximately 55 astronomical units, WIRED reported, a distance measured against the average Earth-sun span of one astronomical unit. Its mass is estimated at 1.9 to 4.0 times that of Jupiter, though researchers believe its volume is likely smaller than Jupiter's, according to the outlet.

Elias 2-24b by the numbers

• Age: Under 1 million years old
• Distance from Earth: About 450 light-years
• Orbital distance: Roughly 55 astronomical units from its star
• Estimated mass: 1.9 to 4.0 times Jupiter's mass

How does this compare to other young exoplanets?

Before this confirmation, the youngest exoplanets found through direct observation orbited the stars PDS 70 and WISPIT 2, both more than 5 million years old, WIRED reported. Elias 2-24b breaks that record by a wide margin, giving astronomers a planet still embedded in the earliest stages of formation rather than one that has already settled into a more mature state.

Why does this discovery matter for planet formation theories?

Elias 2-24b's characteristics challenge elements of the "core accretion model," one of the standard theories of how giant planets form, according to WIRED. That model holds that giant planets form when a solid core grows massive enough to pull in surrounding gas. The planet's extreme youth, combined with its size and orbital distance, gives researchers a rare real-time data point for testing how quickly — and by what mechanism — gas giants can take shape around a young star.

Most of the roughly 6,000 confirmed exoplanets to date are billions of years old, WIRED noted, not because young planets are rare but because older planets are easier to detect using common methods such as the transit method, which spots the dimming of starlight as a planet passes in front of it. Newly formed planets are typically still buried inside the gas-and-dust disks left over from their star's formation, making them far harder to isolate and confirm.

What terms explain this discovery?

• Protoplanetary disk: The disk of leftover gas and dust surrounding a young star, from which planets form.
• Coronagraph data: Telescope imaging that blocks a star's central light so dimmer objects nearby, including planets, become visible.
• Transit method: A common planet-detection technique that measures the slight dimming of starlight as a planet crosses in front of its star.
• Core accretion model: A leading theory of giant-planet formation holding that a solid core grows large enough to attract surrounding gas.

The confirmation gives astronomers a new benchmark for studying planet formation at its earliest stage, before a system has had time to settle into the kind of mature, billions-of-years-old arrangement seen in the solar system.